Why is my furnace running but blowing cold air?
Fan settings, restricted airflow, or an incomplete heating cycle are common causes; combustion components require qualified service.
Urgency: urgent
What this means
Set the thermostat to Heat and fan to Auto, then inspect the accessible filter.
Safe checks
- Confirm thermostat mode
- replace only the same-size filter with the airflow arrow correct
- keep supply and return grilles open.
Stop and get help if
- Leave immediately for a CO alarm or gas odour. Call HVAC service if heat does not return after settings and filter checks.
Which professional to call
Contact the matched licensed or qualified trade if safe checks do not resolve the issue.
Find the relevant tradeSource and method
This answer combines HomeSOS's structured triage with safety boundaries supported by a public source. It does not replace inspection.
Health Canada: Home safety and indoor air guidanceReviewed August 12, 2026